When radio communication is performed, presence of an interfering radio wave is a factor in degrading communication quality. Therefore, a state of interference of the radio wave is monitored, and a measure to reduce the interference of the radio wave is taken. As the measure to reduce the interference, there is, for example, a method of controlling the output of the radio wave, a method of changing an installation location of an apparatus outputting the radio wave, or the like. An effective measure differs depending on properties of the interfering radio wave.
The properties of the radio wave depend on specifications defined in a radio standard, such as parameters used for modulation and a method of controlling the radio wave. It therefore becomes easy to find an effective measure to reduce the interference of the radio wave when the radio standard of the radio wave flying around in the air may be identified. Incidentally, radio standards include Bluetooth (registered trademark; hereinafter BT), Bluetooth low energy (BLE), wireless local area network (WLAN), and ZigBee (registered trademark; hereinafter ZB).
As a method of identifying a radio standard, there is, for example, a method of identifying a radio standard corresponding to a received wave by preparing preamble reference signals corresponding to respective radio standards, and evaluating cross-correlations between the received wave and the preamble reference signals. In this method, processing of calculating a cross-correlation value between the received wave and a preamble reference signal (sliding correlation operation) is executed on a section where the power of the received wave is equal to or higher than a certain value. When the section where the sliding correlation operation is executed is long, a long time is taken to detect a signal component (modulated wave) included in the received wave.
Radio standards such as BT, BLE, and ZB are adopted by many power saving devices. In these radio standards, a long non-modulation section than that of WLAN or the like is set with an intention of stabilizing a transmission signal. A non-modulated wave (continuous wave (CW)) is transmitted in a non-modulation section. Then, in a modulation section subsequent to the non-modulation section, a modulated wave corresponding to a radio standard (modulated wave including a known preamble signal) is transmitted. For example, a modulated wave modulated by a modulation system such as frequency shift-keying (FSK) is transmitted. The above-described sliding correlation operation is executed also on CW. Thus, when there is a long non-modulation section, unnecessary operation is increased.
Incidentally, a pulse analyzer is proposed which avoids a risk of a pulse detector mistaking CW for a pulse due to a transient variation in CW. This pulse analyzer prepares a threshold value for pulse detection and a threshold value for CW detection separately from each other, and uses the threshold value for CW detection when detecting CW. In addition, a method is proposed which identifies whether a received signal is binary phase modulated, non-modulated, chirp modulated, or frequency hopping modulated, and avoids unnecessary operation when the received signal is binary phase modulated or non-modulated. In addition, a code division multiple access (CDMA) receiving device is proposed which preferentially sets, as an object of orthogonalization, a received signal having a large product of a cross-correlation value between spread codes and a reception level.
Examples of the related art include Japanese Laid-open Patent Publication No. 2004-191090, Japanese Laid-open Patent Publication No. 2000-196687, and Japanese Laid-open Patent Publication No. 09-64846.